Abrasive grindstone

ABSTRACT

An abrasive grindstone that includes diamond abrasive grains and a boron compound and that is for grinding a workpiece, wherein the average particle diameter X of the diamond abrasive grains is in the range of 3 μm≦X≦10 μm, and the average particle diameter ratio Z of the boron compound to the diamond abrasive grains is 0.8≦Z≦3.0. Preferably, the workpiece is an SiC wafer, and the average particle diameter ratio Z is in the range of 1.2≦Z≦2.0.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an abrasive grindstone for grinding a workpiece.

Description of the Related Art

In order to grind substrates used for semiconductor production, abrasive grindstones based on the addition of a boron compound are used (see, for example, Japanese Patent Laid-Open No. 2012-056013). The boron compound has solid lubricity and, therefore, has an effect of suppressing the generation of heat at a processing point and the consumption of the grindstone which both arise from grinding.

SUMMARY OF THE INVENTION

The abrasive grindstone disclosed in Japanese Patent Laid-Open No. 2012-056013, however, has a problem that in the case of grinding a hard substrate (for example, SiC substrate), processing load on the grindstone is high, so that the consumption amount of the grindstone is large and the frequency of replacement of the grindstone is high. In addition, in the case of grinding a material that is poor in thermal conductivity such as glass, it is impossible to enhance the processing speed, because of the need to restrain accumulation of heat generated due to the processing. In view of this problem, it is required of an abrasive grindstone to achieve an enhanced productivity while maintaining good processing characteristics as to a workpiece.

Accordingly, it is an object of the present invention to provide an abrasive grindstone with which at least one of a reduction in processing load and a prolongation of service life can be achieved.

In accordance with an aspect of the present invention, there is provided an abrasive grindstone for grinding a workpiece, wherein the abrasive grindstone includes diamond abrasive grains and a boron compound in a predetermined volume ratio, the average particle diameter X of the diamond abrasive grains is in the range of 3 μm≦X≦10 μm, and the average particle diameter ratio Z of the boron compound to the diamond abrasive grains is in the range of 0.8≦Z≦3.0.

Preferably, the workpiece as an object of grinding by the abrasive grindstone is an SiC wafer, and the average particle diameter ratio Z is in the range of 1.2≦Z≦2.0.

With the abrasive grindstone according to the present invention, it is possible, while enhancing the quality of processing by controlling the ratio of the particle diameter of a boron compound to the particle diameter of the diamond abrasive grains (particle diameter ratio), to achieve a lowering in processing load on the abrasive grindstone, enhancement of heat radiation properties, and a prolongation of service life (a reduction in consumption amount) of the abrasive grindstone.

The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a configuration example of a grinding apparatus to which an abrasive grindstone according to an embodiment of the present invention has been applied;

FIG. 2 is a diagram depicting consumption rate (%) of an abrasive grindstone for rough grinding plotted against average particle diameter of a boron compound; and

FIG. 3 is a diagram depicting maximum grinding load of an abrasive grindstone for rough grinding plotted against average particle diameter of the boron compound.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An embodiment for carrying out the present invention will be described in detail below referring to the drawings. The present invention is not to be limited to or by the contents of the following description of the embodiment. In addition, the components described below include those which can be thought by a person skilled in the art and those which are substantially equivalent to the described ones. Further, the following configurations can be combined as required. Besides, omission, replacement or modification of the configurations can be performed without departing from the scope of the gist of the present invention.

Embodiment

FIG. 1 illustrates a configuration example of a grinding apparatus to which an abrasive grindstone according to an embodiment of the present invention has been applied. Note that an X-axis direction in the figure is a width direction of the grinding apparatus 10, a Y-axis direction is a depth direction of the grinding apparatus 10, and a Z-axis direction is the vertical direction.

As depicted in FIG. 1, the grinding apparatus 10 includes: a first cassette 11 and a second cassette 12 in each of which a plurality of wafers W as workpieces are accommodated; common carrying in/carrying-out means 13 serving as both carrying-out means for carrying out the wafer W from the first cassette 11 and carrying-in means for carrying the ground wafer W into the second cassette 12; positioning means 14 for positioning the center of the wafer W; carrying means 15 and 16 for carrying the wafer W; three chuck tables 17 to 19 for suction holding the wafer W; a turntable 20 that rotates with the chuck tables 17 to 19 mounted thereon in a rotatable manner; grinding means 30 and 40 as processing means for applying a grinding treatment as processing to the wafer W held on each of the chuck tables 17 to 19; cleaning means 51 for cleaning the ground wafer W; and cleaning means 52 for cleaning of the chuck tables 17 to 19 after grinding.

In the grinding apparatus 10, the wafer W accommodated in the first cassette 11 is fed by a carrying-out operation of the carrying-in/carrying-out means 13 to the positioning means 14, where center positioning is conducted, after which the wafer W is carried to and mounted on one of the chuck tables 17 to 19, in this figure the chuck table 17, by the carrying means 15. The three chuck tables 17 to 19 in this embodiment are disposed at regular intervals along the circumferential direction of the turntable 20, are rotatable individually, and are moved on an X-Y plane as the turntable 20 rotates. The chuck tables 17 to 19, with the wafer W suction held thereon, are each positioned directly under the grinding means 30 by rotation by a predetermined angle, for example, 120 degrees counterclockwise.

The grinding means 30 is for rough grinding of the wafer W held on each of the chuck tables 17 to 19, and is provided on a wall part 22 disposed upright at an end portion of a base 21 in the Y-axis direction. The grinding means 30 is supported by a support part 33 which is guided by a pair of guide rails 31 disposed on the wall part 22 along the Z-axis direction and which is moved upward and downward by driving of a motor 32. The grinding means 30 is moved upward or downward as the support part 33 is moved upward or downward. The grinding means 30 includes: a motor 34 for rotating a spindle 34 a supported in a rotatable manner; and a grinding wheel 36 which is mounted to a tip of the spindle 34 a through a wheel mount 35 and which grinds the back side of the wafer W. The grinding wheel 36 is provided with grindstones 37 for rough grinding that are firmly attached to its lower surface in a circular annular pattern. Note that rough grinding is grinding of the wafer W to a desired thickness.

The rough grinding is conducted as follows. The grinding wheel 36 is rotated by rotation of the spindle 34 a by the motor 34 and is subjected to grinding feeding downward in the Z-axis direction, to bring the rotating grindstones 37 into contact with the back side of the wafer W, which is held on the chuck table 17 and positioned directly under the grinding means 30, whereby the back side of the wafer W is ground. Here, when the rough grinding of the wafer W held by the chuck table 17 is finished, the turntable 20 is rotated counterclockwise by a predetermined angle, whereby the wafer W having been rough ground is positioned directly under the grinding means 40.

The grinding means 40 is for finish grinding of the wafer W held on each of the chuck tables 17 to 19, and is supported by a support part 43 which is guided by a pair of guide rails 41 disposed on the wall part 22 in the Z-axis direction and which is moved upward and downward by driving of a motor 42. The grinding means 40 is moved upward or downward in the Z-axis direction as the support part 43 is moved upward or downward. The grinding means 40 includes: a motor 44 for rotating a spindle 44 a supported in a rotatable manner; and a grinding wheel 46 which is mounted to a tip of the spindle 44 a through a wheel mount 35 and which grinds the back side of the wafer W. The grinding wheel 46 is provided with grindstones 47 for finish grinding that are firmly attached to its back surface in a circular annular pattern. In other words, the grinding means 40 is the same as the grinding means 30 in fundamental configuration, and is different from the grinding means 30 only in the kind of the grindstones 37 and 47. Note that finish grinding is to thin the wafer W to a desired thickness and to remove grinding marks generated on the back side of the wafer W by the rough grinding.

The finish grinding is performed as follows. The grinding wheel 46 is rotated by rotation of the spindle 44 a by the motor 44 and is subjected to grinding feeding downward in the Z-axis direction, to bring the rotating grindstones 47 into contact with the back side of the wafer W, which is held on the chuck table 17 and positioned directly under the grinding means 40, whereby the back side of the wafer W is ground. Here, when the finish grinding of the wafer W held on the chuck table 17 is finished, the turntable 20 is rotated counterclockwise by a predetermined angle, to be returned into an initial position depicted in FIG. 1. In this position, the wafer W whose back side has been finish ground is carried by the carrying means 16 to the cleaning means 51, where grinding chips are removed by cleaning, after which the wafer W is carried into the second cassette 12 by a carrying-in operation of the carrying-in/carrying-out means 13. Note that the cleaning means 52 cleans the chuck table 17 from which the finish ground wafer W has been taken out by the carrying means 16 and which is in a vacant state. Note that grinding chips removal and finish grinding for the wafers W held on the other chuck tables 18 and 19 and the carrying-in/carrying-out of the wafers W from/to the chuck tables 18 and 19 are performed in the similar manner according to the rotation position of the turntable 20.

Preferably, the wafer W to be ground by the grindstone according to the present embodiment is an SiC (silicon carbide) wafer including SiC. An SiC wafer is harder than a wafer including silicon.

Here, the grindstones 37 and 47 for respectively applying rough grinding and finish grinding to the wafer W which is an SiC wafer are each configured by binding diamond abrasive grains and a boron compound together by a bond. The diamond abrasive grains are abrasive grains of at least one of natural diamond, synthetic diamond and metal-coated synthetic diamond. Besides, the boron compound is at least one of B₄C (boron carbide), CBN (cubic boron nitride) and HBN (hexagonal boron nitride). The abrasive grindstones 37 and 47 are each configured by kneading the diamond abrasive grains and the boron compound by use of one of a vitrified bond, a resin bond and a metal bond, and fixing the kneaded mixture by sintering or nickel plating. Preferably, the volume ratio of the diamond abrasive grains and the boron compound is in the range of from 1:1 to 1:3.

Let the average particle diameter of the boron compound be Y [μm] and the average particle diameter of the diamond abrasive grains be X [μm], then the average particle diameter ratio Z (=Y/X) of the boron compound to the diamond abrasive grains in the abrasive grindstone 37 is in the range of 0.8≦Z≦3.0. Here, the average particle diameter ratio Z is set to be not less than 0.8 because if it is less than 0.8, the function or role of the boron compound as a structural material (filler) that embrittles the abrasive grindstone 37 increases. On the other hand, the average particle diameter ratio is set to be not more than 3.0 because if it exceeds 3.0, the diamond abrasive grains which are the principal abrasive grains have a greater function or role as a structural material than a function or role as abrasive grains, and, therefore, become less contributing to grinding. Besides, the average particle diameter X of the diamond abrasive grains is in the range of 3 μm≦X≦10 μm. Here, the average particle diameter X of the diamond abrasive grains is set to be not more than 10 μm because it is suitable for diamond abrasive grains having an average particle diameter X of not more than 10 μm to be used for grinding of the wafer W that is an SiC wafer harder than a silicon wafer formed with electronic devices.

In this embodiment, the average particle diameter X of the diamond abrasive grains in the abrasive grindstone 37 for rough grinding of the wafer W that is an SiC wafer is preferably in the range of 3 μm≦X≦10 μm. If diamond abrasive grains having an average particle diameter X of less than 3 μm are used for the abrasive grindstone 37 for rough grinding, the time required for the rough grinding becomes longer and the abrasive grindstone 37 becomes more brittle. The average particle diameter X of the diamond abrasive grains in the abrasive grindstone 47 for finish grinding of the wafer W that is an SiC wafer is preferably smaller than the average particle diameter of the abrasive grindstone 37 for rough grinding, and is in the range of, for example, 0.5 μm≦X≦1 μm.

As aforementioned, where the average particle diameter ratio Z of the boron compound to the diamond abrasive grains is in the range of 0.8≦Z≦3.0 and the average particle diameter X of the diamond abrasive grains is in the range of 3 μm≦X≦10 μm, the characteristic property of solid lubricity of the boron compound is displayed effectively, whereby processing load on the abrasive grindstone 37 can be lowered, at the time of grinding the wafer W. Therefore, with the processing load on the abrasive grindstone 37 thus reduced, the consumption amount of the abrasive grindstone 37 at the time of grinding a single sheet of wafer W by the abrasive grindstone 37 can be reduced, resulting in a prolonged service life of the abrasive grindstone 37. In addition, the generation of heat at a processing point at the time of grinding the workpiece by the abrasive grindstone 37 can be suppressed, so that the grinding speed can be enhanced, leading to an enhanced productivity. Accordingly, the degree of consumption of the abrasive grindstone 37 in the grinding apparatus 10 is suppressed to a low level, the frequency of replacement of the grindstones can be lowered, and the productivity of the whole grinding process of the grinding apparatus 10 can be enhanced. Since the abrasive grindstone 37 has an average particle diameter ratio Z in the range of 0.8≦Z≦3.0, at least one of a reduction in processing load and a prolongation of service life can be achieved.

In addition, in this embodiment, it is preferable that the abrasive grindstone 37 for rough grinding of the wafer W that is an SiC wafer has an average particle diameter ratio Z in the range of 1.2≦Z≦3.0. In this case, as to the abrasive grindstone 37, consumption during grinding can be suppressed, and a prolonged service life can be achieved.

Besides, in this embodiment, it is more preferable that the abrasive grindstone 37 for rough grinding of the wafer W that is an SiC wafer has an average particle diameter ratio Z in the range of 0.8≦Z≦2.0. In this case, as to the abrasive grindstone 37, a reduction in processing load can be achieved.

Furthermore, in this embodiment, it is further preferable that the abrasive grindstone 37 for rough grinding of the wafer W that is an SiC wafer has an average particle diameter ratio Z in the range of 1.2≦Z≦2.0. In this case, in regard of the abrasive grindstone 37, both a reduction in processing load and a prolongation of service life can be achieved.

In the next place, the present inventors, for confirming the effect of the present invention, produced abrasive grindstones 37 for rough grinding that had different boron compound average particle diameters, and consumption rate of the abrasive grindstones 37 and maximum grinding load during rough grinding of the wafer W that is an SiC wafer were measured. The results are depicted in FIGS. 2 and 3. FIG. 2 is a diagram depicting consumption rate (%) of the abrasive grindstone for rough grinding plotted against average particle diameter of the boron compound. FIG. 3 is a diagram depicting maximum grinding load (N) on the abrasive grindstone for rough grinding plotted against average particle diameter of the boron compound.

The abrasive grindstones 37 for rough grinding used in FIGS. 2 and 3 were each produced by using CBN as the boron compound, kneading the CBN with diamond abrasive grains while using a bond containing SiO₂ as a main constituent, and sintering the kneaded mixture. Out of the abrasive grindstones 37 for rough grinding used in FIGS. 2 and 3, the average particle diameter X of the diamond abrasive grains was 4 μm, the volume ratio of the boron compound and the diamond abrasive grains was 1:1, and the average particle diameter Y of the boron compound was varied within the range of from 3 μm to 20 μm.

The axis of abscissas in FIGS. 2 and 3 represents the average particle diameter Y of the boron compound and the average particle diameter ratio Z. The axis of ordinates in FIG. 2 represents consumption rate of the abrasive grindstone 37. The consumption rate means consumption rate (%) of the abrasive grindstone 37 in relation to the actual grinding amount. The axis of ordinates in FIG. 3 is maximum (N) of the load exerted during rough grinding. In FIGS. 2 and 3, a plurality of abrasive grindstones 37 for rough grinding containing the boron compound of the same average particle diameter Y were produced, and measurement of consumption rate and maximum grinding load during rough grinding of an SiC wafer as a workpiece while using each of the abrasive grindstones was conducted. Note that in FIGS. 2 and 3, average values of consumption rate and maximum grinding load are indicated by dotted lines.

According to FIG. 2, it was made clear that, where the average particle diameter ratio is not less than 1.2 and not more than 3.0, the consumption rate of the abrasive grindstone 37 can be suppressed to or below approximately 10%, as compared to the case where the average particle diameter ratio Z is below 1.2 or above 3.0. In addition, it was made clear by FIG. 3 that where the average particle diameter Z is not less than 0.8 and not more than 2.0, the maximum grinding load can be suppressed (namely, the processing load can be reduced) as compared to the case where the average particle diameter ratio Z exceeds 2.0. Further, according to FIG. 2, it was made clear that the consumption rate of the abrasive grindstone 37 increases when the average particle diameter ratio Z is less than 0.8.

In this way, according to FIGS. 2 and 3, it was made clear that where the average particle diameter ratio Z of the abrasive grindstone 37 is set to be not less than 0.8 and not more than 3.0, at least one of a prolongation of service life and a reduction in processing load can be achieved, and that where the average particle diameter Z is not less than 1.2 and not more than 2.0, both a prolongation of service life and a reduction in processing load can be achieved.

Note that while the abrasive grindstone 37 is mainly described in the aforementioned embodiment and example, the present invention may be applied to the abrasive grindstone 47 for finish grinding.

The present invention is not limited to the details of the above described preferred embodiment. The scope of the invention is defined by the appended claims and all changes and modifications as fall within the equivalence of the scope of the claims are therefore to be embraced by the invention. 

What is claimed is:
 1. An abrasive grindstone for grinding a workpiece, wherein the abrasive grindstone includes diamond abrasive grains and a boron compound in a predetermined volume ratio, the average particle diameter X of the diamond abrasive grains is in the range of 3 μm≦X≦10 μm, and the average particle diameter ratio Z of the boron compound to the diamond abrasive grains is in the range of 0.8≦Z≦3.0.
 2. The abrasive grindstone according to claim 1, wherein the workpiece is an SiC wafer, and the average particle diameter ratio Z is in the range of 1.2≦Z≦2.0.
 3. The abrasive grindstone according to claim 1, wherein the predetermined volume ratio of the diamond abrasive grains and the boron compound is in the range of from 1:1 to 1:3.
 4. The abrasive grindstone according to claim 1, wherein the boron compound is selected from the group consisting of boron carbide, cubic boron nitride and hexagonal boron nitride. 